Methods for increasing the usable position error signal (PES) region

ABSTRACT

Methods are provided for selecting write elements, that can be used in a media-writer, for writing servo burst patterns that have a desired width. Methods for writing preferred servo patterns are also provided. Methods for controlling a write current to produce servo bursts have a desired width are also provided. In accordance with specific embodiments of the present invention, the desired burst width is three-fourths of a data track wide. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures and the claims.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to commonly assigned U.S. patentapplication Ser. No. ______, (Attorney Docket No. PANAP-01048US1),SYSTEMS AND ROTATABLE MEDIA FOR INCREASING THE USABLE POSITION ERRORSIGNAL (PES) REGION, which was filed the same day as the presentapplication, and which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to rotatable media data storagedevices, such as hard disk drives.

BACKGROUND OF THE INVENTION

Advances in data storage technology have provided for ever-increasingstorage capability in devices such as DVD-ROMs, optical drives, and diskdrives. In hard disk drives, for example, the width of a written datatrack has decreased due in part to advances in reading, writing, andpositioning technologies. Narrower data tracks result in higher densitydrives, which is good for the consumer but creates new challenges fordrive manufacturers. For example, as data tracks are narrowed, so arethe read elements used to read the tracks. However, as read elementsbecome narrower, and previously-used head-width tolerances become moredifficult to achieve, controlling position error signal (PES) linearitybecomes more difficult. Accordingly, it is desirable to provide for PESlinearity improvements, e.g., by increasing the useable PES region.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a schematic representation of an MR read element juxtaposednext to two radially offset, radially trimmed bursts.

FIG. 1B is a graph of burst amplitude difference as a function of MRread-element radial displacement from a burst-established trackcenterline for the FIG. 1A trimmed burst pattern.

FIG. 2A is a schematic representation of an MR read element juxtaposednext to two radially offset, untrimmed bursts.

FIG. 2B is a graph of burst amplitude difference as a function of MRread-element radial displacement from a burst-established trackcenterline for the FIG. 2A untrimmed burst pattern.

FIG. 3 is a greatly enlarged, planarized diagrammatic plan of atwo-step-per-data-track (also known as two-pass-per-data track)untrimmed reference servo burst pattern, according to an embodiment ofthe present invention.

FIG. 4A is a graph of burst amplitude difference as a function of MRread-element radial displacement from a burst-established trackcenterline for the untrimmed burst pattern of FIG. 3. FIGS. 4B-4F areuseful for explaining how portions of the curve in FIG. 4A correspond todifferent radial positions of a read element.

FIG. 5A is an exemplary plot showing the variation of burst width as afunction of write-current for a write element. FIG. 5B is a diagramschematically illustrating how a write-head's magnetic field linesbeyond a specified field-strength vary with write current.

FIG. 6 is a diagram showing a burst pattern that can be used tocalibrate a servowriting process in accordance with an embodiment of thepresent invention.

FIG. 7 is a high level block diagram of an exemplary media-writerstation.

FIG. 8A is a high level flow diagram useful for describing methods ofthe present invention that can be used with media-writers.

FIG. 8B is high level flow diagram useful for describing embodiments ofthe present invention where a write current is controlled to produceservo bursts having a desired width.

FIG. 9A is a high level block diagram of an exemplary head disk assemblylocated at a servowriter station.

FIG. 9B is a high level block diagram of the exemplary head diskassembly of FIG. 9A, after it has been sealed and provided with a driveelectronic circuit board to produce a complete disk drive assembly.

SUMMARY OF THE INVENTION

Some embodiments of the present invention are directed to methods forselecting write elements, that can be used in a media-writer, forwriting servo burst patterns that have a desired width. Embodiments ofthe present invention are also related to servo writers that produceservo burst having a desired width.

In accordance with embodiments of the present invention, a desired servoburst width is equal to three-fourths of a track width. In accordancewith embodiments of the present invention, the servo bursts areuntrimmed. The servo burst patterns, according to embodiments of thepresent invention, preferably provide for an increased useable positionerror signal (PES) region.

Embodiments of the present invention also relate to producing servobursts having a desired width by controlling a write current provided toa write element. The write current can be controlled within a mediawriter, in accordance with embodiments of the present invention. Inother embodiments, a servowriter controls the write current. In stillother embodiments, the write current is controlled during self servowriting. Embodiments of the present invention also relate to preferredservo burst patterns.

Embodiments of the present invention also relate to rotatable storagemedia (e.g., disks) that include preferred servo burst patterns. Inaccordance with certain embodiments of the present invention, thepreferred servo burst patterns include untrimmed servo bursts that aresubstantially three-fourths of a desired data track width in radialextent. Embodiments of the present invention also relate to methods forproducing preferred servo burst patterns, as well as systems thatinclude rotatable storage media including preferred servo burstpatterns.

This summary is not intended to be a complete description of, or limitthe scope of, the invention. Further embodiments, features, aspects, andadvantages of the present invention will become more apparent from thedetailed description set forth below, the drawings and the claims.

DETAILED DESCRIPTION OF THE INVENTION

The information stored on a disk can be written in concentric tracks,extending from near the inner diameter of the disk to near the outerdiameter of the disk. In an embedded servo-type system, servoinformation can be written in servo wedges, and can be recorded ontracks that can also contain data. In a system where an actuatorassembly arm rotates about a pivot point such as a bearing, the servowedges may not extend linearly from the inner diameter (ID) of the diskto the outer diameter (OD), but may be curved slightly in order toadjust for the trajectory of the head as it sweeps across the disk.

The servo information often includes bursts of transitions called “servobursts,” a group of which can be used to form a burst pattern. The servoinformation can be positioned regularly about each track, such that whena head reads the servo information, a relative position of the head canbe determined that can be used by a servo processor to adjust theposition of the head relative to the track. For each servo wedge, thisrelative position can be determined in one example as a function of thetarget location, a track number read from the servo wedge, and theamplitudes or phases of the bursts, or a subset of those bursts. Thesignal that is indicative of the position of a head or element, such asa read/write head or element, relative to the center of a target track,will be referred to herein as a position-error signal (PES).

For example, a centerline for a given data track can be “defined”relative to a series of bursts, burst edges, or burst boundaries. Thecenterline can also be defined by, or offset relative to, any functionor combination of bursts or burst patterns. This can include, forexample, a location at which the PES value is a maximum, a minimum, or afraction or percentage thereof. Any location relative to a function ofthe bursts can be selected to define track position. For example, if aread element evenly straddles an A-burst and a C-burst, or portionsthereof, then servo demodulation circuitry in communication with theread element can produce equal amplitude measurements for the twobursts, as the portion of the signal coming from the A-burst above thecenterline is approximately equal in amplitude to the portion comingfrom the C-burst below the centerline. The resulting computed PES can bezero if the radial location defined by the A-burst/C-burst (A/C)combination, or A/C boundary, is the center of a data track, also knownas a track centerline. In such an embodiment, the radial location atwhich the PES value is zero (e.g., where A-C=0) can be referred to as anull-point. Null-points can be used in each servo wedge to define arelative position of a track. If the head is too far towards the outerdiameter of the disk, or above the centerline, then there will be agreater contribution from the A-burst that results in a more “negative”PES. Using the negative PES, the servo controller could direct the voicecoil motor to move the head toward the inner diameter of the disk andcloser to its desired position relative to the centerline. This can bedone for each set of bursts defining the shape of that track about thedisk. Exemplary track centerlines are discussed in more detail belowwith reference to FIGS. 1A and 1B. It is noted that a burst labeled “C”in this application, which is generally 180 degrees out of phase from an“A” burst, may in some other documents and patents be referred to as a“B” burst. Accordingly, the present invention should not be limited bythe specific choice of labeling servo bursts.

The PES scheme described above is one of many possible schemes forcombining the track number read from a servo wedge and the phases oramplitudes of the servo bursts. Many other schemes are also possible.

A disk drive can have tens of thousands of data tracks, with each trackincluding embedded servo information or patterns. There are numeroustechniques for writing these servo patterns, some of which are discussedbelow. One such technique uses a media-writer, which is well known inthe art, to write servo patterns on a stack of disks. Each disk is thenplaced in a separate drive containing multiple blank disks, such thatthe drive can use the patterned disk as a reference to re-write servopatterns on all of the other disk surfaces in the drive, as well aswriting a servo pattern on the patterned surface, if desired. It is alsopossible that the media writer is used to write the final patterns onthe disk surface(s). Such disks can then be placed in disk drives andused “as is” (i.e., without re-writing of servo patterns). Media-writersare relatively expensive instruments, and they may take a long time towrite a reference pattern or final pattern on a stack of disks. However,if the stack contains ten blank disks, for example, then themedia-writer can write the reference pattern for ten drives inapproximately the same time that it would have taken to servowrite asingle drive. If a servo-pattern thus produce is used as a referencesurface for self-serowriting of that and/or other surfaces in thedriver, this scheme is a member of a class of self-servowritingtechniques commonly known as “replication” self-servowriting.

A typical replication process, in which a drive servos on the referencepattern and writes final servo patterns on all surfaces, takes placewhile the drive is in a relatively inexpensive test-rack, connected toonly a power-supply. The extra time that it takes is therefore usuallyacceptable.

Another class of self-servowriting techniques is known as “propagation”self-servowriting. Schemes in this class differ from those in the“replication” class in the fact that the wedges written by the drive atone point in the process are later used as reference wedges for othertracks. These schemes are thus “self-propagating”. Typically, suchschemes require a R/W head that has a large radial offset between theread and write elements, so that the drive can servo with the readelement over previously-written servo wedges while the write element iswriting new servo wedges. In one such application, a servowriter is usedfor a short time to write a small “guide” pattern on a disk that isalready assembled in a drive. The drive then propagates the patternacross the disk. In this type of self-servowriting operation, previouslywritten tracks can later serve as reference tracks.

As described in U.S. patent application Ser. No. 10/923,662, entitledSYSTEMS AND METHODS FOR REPAIRABLE SERVO BURST PATTERNS (Attorney DocketNo. PANA-01067USD), filed Aug. 20, 2004, which is incorporated herein byreference, many self-servowriting techniques require a three or morestep-per-track servowriting process to provide a more linear (or atleast, a linearizable) PES at all locations along a track. As will bedescribed below, specific embodiments of the present invention enableservo burst patterns to be written during a two-step-per-trackservowriting process (also known as a two-pass-per-track scheme), whichis preferred to a three or more -step-per-track scheme, because the lesssteps per track, the faster the servo information can be written onto adisk.

As explained in U.S. Pat. No. 6,519,107, which is incorporated herein byreference, an initial issue confronting a disk drive designer is whetherto employ “trimmed bursts” or “untrimmed bursts”. A trimmed servo burstis one in which a radial edge of the burst is DC erased during asubsequent pass of the write element at a displaced radial positionrelative to the disk. A trimmed burst pattern is shown in FIG. 1Awherein a servo burst A′ has a lower radial edge which has been trimmed(the portion of the A′ burst enclosed in the dashed line block has beenDC erased) to be in approximate alignment with the upper radial edge ofan adjacent burst C′. The bursts A′ and C′ are written using a R/W head104, which includes a write element 106 and a magneto-resistive (MR)read element 105. It is possible to trim a previously written burst,such as burst A′ during a single pass of the write element 106 along aservowriting path for writing the C′ burst. However, it has beendiscovered that a repeatable runout error (RRO) can be reduced by afactor of about the square root of two when an untrimmed burst patternis used in lieu of a single-pass-trimmed burst pattern. It is believedthat the burst null point for an untrimmed burst pattern is determinedby non-repeatable runout error (NRRO) of two different servowritingpasses (one pass for each burst written), while the burst-null-point fora trimmed pattern as shown in FIG. 1A is determined by the NRRO of asingle pass (wherein the write element trims one burst and writesanother burst). While the FIG. 1A trimmed-burst pattern could be writtenin a way to reduce its RRO by the square root of two factor by requiringtwo passes for each burst: one pass to trim the previous burst and asecond pass to write the burst, such an approach, if executed on aservowriter or media-writer, would nearly double the servowriting time.

FIG. 1B graphs a PES which is linear as a function of radial offset ofthe MR read element 105 about a centerline (A-C) passing through theapproximately aligned edges of the A′ and C′ trimmed bursts. If thewrite element 106 is about one track wide, then the PES linearity signalshould be about the same for trimmed or untrimmed servo bursts. However,for write elements, which have electrical writing widths greater or lessthan about one track width, the useable portion of the PES curve islarger for untrimmed bursts. FIGS. 1A and 1B show the A′-C′ PES as afunction of radial displacement of the MR read element 105 for the twotrimmed bursts A′ and C′. The idealized curve presented as FIG. 1B has alinear portion, bounded on both sides by flat lines. The useable portionof the FIG. 1B curve is simply the linear portion of the curve.

FIGS. 2A and 2B show an equivalent situation for untrimmed bursts A andC, written using a R/W head 204, which includes a write element 206 anda read element 205. The linear portion of the FIG. 2B curve, centeredabout A-C=0, is smaller than that of the trimmed burst pattern, but theuseable, non-flat portion of the FIG. 2B curve extends over a largerradial displacement of the MR read element 205 relative to the disk. Ifa PES linearization method is used to re-linearize the PES within thedrive servo loop, then the FIG. 2A untrimmed burst pattern has a largeruseable region. An exemplary manufacturing process for determination ofa PES linearization table, which is disclosed in U.S. Pat. No. 6,369,971(Everett), is incorporate by reference. Other PES linearization schemesare also available, such as, but not limited to, those disclosed in U.S.Pat. No. 5,982,173 (Hegan). While FIGS. 2A and 2B show overlappeduntrimmed A and C bursts, similar reductions in the RRO and increases inthe non-flat usable PES region are achieved if the untrimmed A and Cbursts underlap (e.g., as shown in FIG. 3, discussed below).

Preferred Burst Patterns

In accordance with embodiments of the present invention, a preferredservo burst width for a two-step-per-data track (also known astwo-pass-per-track) untrimmed burst pattern is three-fourths of adesired data track width (DTW). Embodiments of the present invention arealso directed to systems and methods for efficiently writing servo burstpatterns that have the preferred burst widths.

One way to write burst patterns having a desired burst width (e.g., thepreferred burst width) is to use a write element having a width that,given a predetermined write current, will produce burst widths that aresubstantially equal to the desired burst width. However, as a practicalmatter, the manufacturing of write elements will produce write elementshaving a distribution of widths. In other words, even after an optimumwrite element width is determined, there is currently no efficientmanufacturing technique that will ensure that all or most of the writeelements that are manufactured will have the optimum width. For example,even if write elements were specifically manufactured with the goal ofproducing burst widths that are three-fourths of a data track wide, fora given write current, it is possible that only about 10% of themanufactured write elements will achieve this very tight tolerance.Clearly, it would be too costly to dispose of the other 90% of the writeelements that do not satisfy the tight tolerance. Even if the situationwere reversed (so that 90% of the manufactured write elements were verynear to the desired width), this would result in 10% of all 1-headdrives having that head being out of tolerance. Worse yet, roughly 19%of all 2-head drives would contain at least one out-of-tolerance head(and so on for drives using more than two heads). Even a 10%yield-reduction would not be tolerable for a high-volume, low-costdrive.

In accordance with an embodiment of the present invention, writeelements are measured and/or tested so that write elements producing adesired burst width (e.g., three-fourths of a data track wide) can beidentified and singled out. These ideal or near ideal write elements arethen used in one or more media-writers to write final servo patterns ondisks. As explained above, media-writers are relatively expensive tostart with. Further, there will be relatively few media-writers ascompared to the number of disk drives produced using the media-writers.Thus, a disk manufacturer can rationalize selecting and using the idealor near ideal write elements in the media-writers.

FIG. 3 is a greatly enlarged, planarized diagrammatic plan view of atwo-step-per-data-track (also known as two-pass-per-data-track)untrimmed servo burst pattern, according to an embodiment of the presentinvention. The servo burst pattern 306 of FIG. 3 can be produced using awrite element that, for a given write current, produces servo burststhat are three-fourths of a data track width. In accordance with anotherembodiment of the present invention, servo bursts that are three-fourthsof a data track width can be produced by appropriately adjusting thewrite current. A further embodiment combines these two ideas. The datatrack width (DTW), which is also known as a data track pitch, is definedas the distance between two data track center lines. Since data trackcenterlines are in actuality defined by servo bursts (or distancesbetween bursts), a data track width (DTW) is actually defined by theservo bursts. Accordingly, when referring to bursts as they are beingwritten, it is more accurate to say that the untrimmed servo bursts, inaccordance with an embodiment of the present invention, arethree-fourths of a desired DTW (since there is no DTW until after theservo bursts are written). The desired DTW is likely predetermined. Anexemplary DTW is 0.25 μm. This is just an example that is not meant tobe limiting. Other data track widths are also within the spirit andscope of the present invention. It is also within the scope of thepresent invention for the desired DTW to vary for different positionsalong a stroke the disk drive (i.e., depend upon the position along thestroke).

As shown in FIG. 3, the servo burst pattern 306 includes four untrimmedservo bursts A, B, C and D. The A, B, C and D bursts are written in twosteps (also known in the art as two passes) per data track, with thewrite element moving one-half of the desired DTW during successive steps(i.e., the write element moves in one-half track pitch steps). Atwo-step-per-track (also known in the art as two-pass-per-track) schemeis preferred to a three-step-per-track (also known in the art asthree-pass-per-track) scheme, because the less steps per track, thefaster the servo information can be written onto a disk.

The servo bursts A, B, C and D are not trimmed (i.e., are un-trimmed),thereby reducing RRO and/or the amount of time necessary to write thebursts. The track centerline can be followed, e.g., by tracking whereA-C=0. Where B-D=0 can be used to indicate one-half of the DTW above orbelow the track centerline, which are the track's radial edges. Suchinformation can be useful when attempting to compensate for thewrite-to-read offset associated with most heads, or during seekingoperations. The track center lines and radial edges can be defined inother manners, as explained below.

It can be observed from FIG. 3 that none of the burst edges are alignedwith a data track centerline (assuming the dashed horizontal linesrepresent the track center lines). It can also be observed that anA-burst and a C-burst do not overlap, and a B-burst and a D-burst do notoverlap. Rather, the A-burst and the C-burst underlap each other byone-fourth (¼) of a DTW. In other words, the lower burst edge of theA-burst is separated (i.e., offset) from the upper edge of the C-burstby one-fourth of a DTW, with each burst being on opposite sides of adata track centerline, enabling a read element to servo where A=C (i.e.,the data track centerline can be where A-C=0). Similarly, the lowerburst edge of a B-burst is separated from the upper edge of a D-burst byone-fourth of a DTW, with the B burst straddling one track centerline(e.g., Tk Ctr. # 0), and the D-burst straddling an adjacent trackcenterline (e.g., Tk Ctr. #1), enabling half tracks to be identified(i.e., half way between two adjacent track centerlines can be whereB-D=0).

As can also be observed from FIG. 3, adjacent bursts overlap one anotherby one-fourth (¼) of a DTW, and upper edges (or lower edges) of adjacentbursts are one-half (½) of a DTW separated from one another. Forexample, an A-burst and adjacent B-burst overlap by one-fourth of a DTW,and the upper edge of the A-burst is separated from the upper edge ofthe B-burst by one-half of a DTW. Such a burst arrangement allows forgood position information at all points (i.e., locations) across a track(so long as the reader width is significantly greater than 25% of a DTW)

Embodiments of the present invention include methods and system forproducing the untrimmed servo burst pattern of FIG. 3. Embodiments ofthe present invention are also directed to rotatable media (e.g., disks)that include the untrimmed servo burst pattern of FIG. 3., as well assystems (e.g., disk drives) that include such rotatable media. This willbe further appreciated from the discussion below.

FIG. 4A shows an exemplary PES curve that can be obtained using theburst pattern shown in FIG. 3. Assume the slope of the PES curve isdefined as a change in burst difference over a change in radial position(i.e., slope=Δ(A-C)/Δr). Also assume that the PES curve is useful (fordetermining the radial locations of a read element) as long as the slopeof the PES curve is not flat (zero or infinite slope).

Looking at the PES curve in FIG. 4A, the portion 402 of the curvecorresponds to those radial positions along the track where a readelement (labeled 405 in FIGS. 4B-4F) reads portions of both the A burstand the C burst, e.g., as shown in FIG. 4B. The portion 404 of thecurve, where the defined slope becomes steeper, corresponds to thoseradial positions along the track where the read element 405 reads the Aburst, without reading the C burst, but the read element 405 overlapsthe gap between the A and C bursts, e.g., as shown in FIG. 4C. Theportion 406 of the curve is where the read element 405 is encompassed bythe A burst, e.g., as shown in FIG. 4D, causing the slope to becomeflat. On the other end of the curve, the portion 408 of the curve iswhere the read element 405 reads the C burst, without reading the Aburst, but the read element 405 overlaps the gap between the A and Cbursts, e.g., as shown in FIG. 4E. The portion 410 of the curve is wherethe read element 405 is encompassed by the C burst, e.g., as shown inFIG. 4F, causing the slope to become flat.

For a given read element width (RW), it is desirable to have the usableportion of a PES curve be as large as possible. As shown in FIG. 4A, byusing the burst pattern of FIG. 3, the usable portion of the PES curveis equal to RW plus one-fourth of a DTW. More specifically, as can beappreciated from FIGS. 4A-4F, the read element 405 can go ½ RW+⅛ DTWabove a track center line, and ½ RW−⅛ DTW below a track center linebefore the slope becomes zero (assuming the slope is defined asΔ(A-C)/Δr), resulting in a useful region equal to RW+¼ DTW. It is alsodesirable the read element “see” two bursts edges when it is close tothe write center line, resulting in lower RRO and PES noise whenwriting.

Assuming that a useful PES is required at all points along a track, aservo burst pattern can define how narrow the width of a read element(RW) can be. Preferably, a burst pattern will allow for as narrow a readelement as possible, thereby allowing as large a range of read elementwidths (RWs) as possible (and thereby, providing more relaxed tolerancesto the vendors of the heads). In other words, if a useful PES can beobtained from a larger range of read element widths, then the headvendors will be allowed more leeway when manufacturing the heads.Further, using a narrow read element is advantageous when readingnon-servo information, i.e., when reading user data. This is because ifthe read element is significantly smaller than the write element used towrite the user data, then more radial displacements (e.g., trackmis-registration) can be tolerated during both writing and reading ofdata without the displacements adversely affecting reading of the data.However, there is a limit to how narrow a read element can be, which isthe point at which the read element is so narrow that a useful PES cannot be obtained. Another limit would be the width below which theuser-data readback signal is too low to permit low-error-rate reading ofthe user data. Using the burst pattern of FIG. 3, it is believed that aread element as narrow as three-eighths of a DTW can be used (i.e., RW≧243/8 DTW).

While burst pair differences (e.g., A-C, and B-D) can be used fortracking centerlines and determining other positions across a track, thepresent invention is not meant to be limited in this manner. Rather,numerous other position schemes have been developed (and may be furtherdeveloped) that use more than two bursts (e.g., three or four bursts) todetermine radial position. It is within the spirit and scope of thepresent invention that such other position schemes can be used with theburst pattern of FIG. 3. For example, the centerline can also be definedby, or offset relative to, any function or combination of bursts orburst patterns. This can include, for example, a location at which thePES value is a maximum, a minimum, or a fraction or percentage thereof.In other words, any location relative to a function of the bursts can beselected to define track position.

As mentioned above, one way to write burst patterns that have a desiredwidth (e.g., three-fourths of a desired DTW) is to identify, throughmeasurements and/or tests, write elements having a width that, given apredetermined write current, will produce burst widths that aresubstantially equal to the desired burst width. A disk manufacturer canrationalize selecting and using the ideal or near ideal write elementsin media-writers, because media-writers are expensive and relatively feware required to produce large quantities of disk drivers.

As also mentioned above, in accordance with another embodiment of thepresent invention, a write current can be selected such that a non-idealwrite element produces burst widths that are substantially equal to thedesired burst width. As shown in the exemplary graph of FIG. 5A, thewritten burst width produced by a write element varies with writecurrent. The dashed line in FIG. 5A illustrates how a write current canbe selected to produce a burst width that is three-fourths (i.e., 75%)of a desired DTW. A table or graph similar to FIG. 5A can be producedfor each write element (e.g., during calibration), and then a precisewrite current can be selected to achieve desired burst widths. Theprecisely selected write current can be used to produce final burstpatterns in a media-writer (i.e., the write currents of write elementsin media-writers can be controlled to produce the desired servo burstwidth). In accordance with another embodiment of the present invention,a precisely selected write current is used to produce the desired servoburst width (BW) during servo-writing performed by a servowriter (e.g.,in a clean room). In still another embodiment, a precisely selectedwrite current is used to produce the desired servo burst width duringself-servo writing.

Various calibration procedures can be used to calibrate a write element.In accordance with an embodiment of the present invention, a writeelement can be calibrated in order to determine the width of a burstwritten by the write element as a function of write current. Thelocation of a write element can be determined by observing a referencepattern. Such reference patterns can include, but are not limited to,patterns written to one surface of a rotatable media by a media-writer,printed-media patterns, or portions of final servo patterns written by adrive during an earlier portion of an ongoing self-servowritingoperation. Calibrated quantities can vary from element to element, andfrom drive to drive. Write widths can also vary, for example, as afunction of radius skew angle of the head and/or temperature, such thatit may not be enough to simply calibrate a write element by varyingwrite current. If a drive or test-process setup does not include thecapability to measure temperature, it may be necessary to operate with arelatively steady power-draw for long enough to attain a steady-statetemperature. The calibrated write width as a function of head-number,write-current, temperature, skew angle and radius can be recorded forlater use. This information can be stored, for example, in memoryresident in a drive or on the drive itself in a reserved location.

One such calibration process that can be used with embodiments of thepresent invention utilizes a DC-erase space in the data-area, betweenservo samples that are used to control the position of a R/W head duringthis test. A field can be written into this erased space that looks likea servo burst using a specific write-current (I₀). A “track-profile” ofthe burst can be determined, such as by scanning the R/W head radiallyacross the written burst, and measuring the burst amplitude as afunction of radial position. The burst amplitude can be measured usingwhatever circuitry and technique the servo normally uses to demodulateservo bursts. The burst could be written immediately after the burstsnormally used by the servo, and the servo demodulation circuitry couldbe re-programmed to demodulate the burst as if it were an extra servoburst. That burst value may not be used by the servo for controlling theposition of a R/W head, but only for calibration purposes. The measuredprofile, which can be a function of the writer width, the write-current,the reader width, and radius, as well as possibly the media propertiesand temperature, will typically have a rising portion (as the readerapproaches the written burst), a relatively flat portion (where thereader is entirely contained within the written burst), and a fallingportion (where the reader is getting out from under the written burst).

These steps can then be repeated using a different write-current (I₁).If I₁ is larger than I₀, then the measured profile should be wider thanthe original profile. It is likely that the wider profile will haverising and falling portions that are essentially parallel to those ofthe original burst, but displaced in position. The difference inposition of the rising and falling portions of the profile can berecorded as a function of the write current. A table can be constructedthat associates the variation of the location of the edges of writtenbursts (i.e., the displacement of the rising or falling portion of thetrack profile) with write-current. This process can be repeated atseveral radial locations for each R/W head. Such a table can be usedlater, e.g., during a self-servowriting process. The drive can use aninterpolation scheme to determine the variation of burst-width withwrite-current using the data in the table. Such a table canalternatively be produced and used by a media-writer or servowriter.

Knowing the calibrated write width as a function of write-current (aswell as other possible variables) allows a media-writer, servo-writer,or drive (during self servo writing) to produce servo bursts having adesired width (e.g., three-fourths of a DTW), in accordance withembodiments of the present invention.

The illustrations in FIG. 5B are intended to show how magnetic fieldlines change with write current. Exemplary field line diagrams are shownfor three different write currents, with the lowest write currentrepresented in the left most sub-figure and the greatest write currentrepresented in the right most sub-figure. At each current, the fluxlines are shown passing from a first pole (P1) to a second pole (P2) ofthe write element. As shown in FIG. 5B, the shape of the field lines maynot vary significantly with write current as long as the write elementis not saturated, only the magnitude of the flux lines. Even ifsaturation does occur to some extent, however, the written burst widthcan still rise monotonically with increasing write current. As such,there is a distance from the head at which the write field decays to alow enough level that it is no longer capable of writing to the media.As the write current is increased, the distance from the write elementat which the field is large enough to write to the media increases aswell. The width of the written bursts therefore can be seen to rise as afunction of the write-current. An illustrative plot of how that burstwidth (BW) can vary as a function of write current for a given writeelement is shown in FIG. 5A, which was discussed above. Still referringto FIG. 5B, to the extent that the write element acts in a linearfashion (which is limited, but worth talking about), the field lineshapes, themselves, do not change. Rather, the field-strengths just growin proportion to the applied write current. Thus, as the write currentis increased, the regions in which the field-strength is beyond athreshold field-strength (which is large enough to change themagnetization of the media) grows in extent. This is recognizable inFIG. 5B, where the field-lines in the progression of sub-figures areidentical to those which are in the same general region as those of anearlier sub-figure, by but with more lines (further out from the poles)as the current grows.

An alternative calibration scheme can be used to determine how theeffective centerline of the servowritten track, as determined by theedges of the written bursts, varies with write current. The way in whichthe centerline of a written track varies with write current can bedetermined by servowriting a track with different write-currents andmeasuring the variation of the track-centerline with the write-current.This approach is illustrated in FIG. 6.

In FIG. 6, it is assumed for the sake of simplicity that writing withthe nominal current would produce untrimmed A and C bursts with thedesired spacing (e.g., ¼ DTW underlap). It is also assumed for the sakeof simplicity that the A bursts are in the correct position when the Cbursts are being written. The write-current can then be intentionallyvaried from wedge to wedge, in a predetermined fashion, to produce arepetitive misplacement of the C bursts. For example, Wedge #0 in FIG. 6is written with a smaller-than-nominal write current, such that theupper edge of the C burst is below the desired position. Wedge #1 andwedge #3 are written with nominal write currents, and wedge #2 iswritten with a larger-than-nominal write current, such that the top edgeof the C burst extends above the desired position. The misplacement ofthe bursts written for wedges 0 and 3 can be determined by servoing onthe servowritten track and applying RRO reduction techniques, such asthose described in the U.S. patent application Ser. No. 10/923,662,which was incorporated by reference.

In fact, the placement of the upper edge of the C bursts will benon-ideal for reasons other than the fact that servowriting is done withvarying write-current. Additionally, the lower edges of the A burstswill in practice not be precisely in the ideal position. Even though anattempt can be made to remove the RRO of the original reference patternbefore servowriting, the RRO might not get completely removed. Also, theNRRO that is being rejected can be present during the calibration and“contaminate” the results. The contamination due to RRO in the referencepattern, which is not completely removed by RRO reduction techniques,can be reduced by doing two processes at a time. In a first process, auniform (nominal) write current can be used to write all wedges. In asecond process, the write current can be varied from wedge to wedge in apre-determined fashion. By comparing the results, or computed trackcenterline placement, of the two processes, the track centerlinedisplacement can better be determined as a function of write current. Inorder to remove effects of NRRO on the calibration, the above processcan be repeated several times. The results of these process repetitionscan then be averaged in order to remove the effects of the random NRRO.While the above procedure involved varying the write current to adjustthe upper edge of the C bursts, a similar procedure can be used to varythe lower edge of the A bursts, or to adjust the position of otherbursts (e.g., B and D bursts)

Exemplary Media-Writer

FIG. 7 is a high level block diagram of an exemplary media-writerstation 700. The media-writer 700 includes an actuator assembly 706, aplurality of read/write (R/W) heads 704, a read/write (R/W) channel 714,a spindle motor (SM) 732 and a voice coil motor (VCM) 730. There can bea single RW head 704 per disk, or a RW head 704 per surface of a disk(i.e., two RW heads 704 per disk). There can be a single R/W channel, orthere can be a separate R/W channel for each of the heads 704. Themedia-writer may also include a current pre-amplifier (not shown)between the heads 704 and each R/W channel 714. A SM driver 712 drivesthe SM 732, and a VCM driver 708 drives the VCM 730. Each R/W head 704includes a write element and a read element.

A plurality of disks 702 are stacked at once on a writer spindle shaft728, with at least one head 704 being provided for each disk 702. An airbearing may be associated with the SM 732 to obtain accurate and stabledisk revolution. Similarly, an air bearing may be associated with theVCM 730 and/or actuator assembly 706. Optical sensors, or the like, canbe used to accurately detect disk revolution. Alternatively, the spindlecontroller can detect the spindle rotation via sensing of back-EMFcrossings of the open-circuit winding of the motor, as is known to oneof ordinary skill in the art. Optical encoder technology, laserinterferometer technology, a capacitative sensor, or the like, can beused to accurately detect the angle of the actuator assembly 706.Tilting components of the spindle 728 and actuator assembly 706 may alsobe controlled. It is also possible that the VCM 730 and actuatorassembly 706 can be replaced with a common cartridge that is controlledby a linear motor, e.g., as described in U.S. Pat. No. 5,012,363, whichis incorporated herein by reference.

A controller 720 controls the SM driver 712, the VCM driver 708, and theR/W channel 714. The controller 712 likely includes, or is incommunications with, a micro-processor. The controller may include aservo controller, a phase lock loop (PLL), and other (or alternative)components for accurately controlling the rotation of the disks 702,positioning of the heads 704, and writing of servo patterns. Forexample, the controller may also include a stable clock system, a writepattern generator, a pattern detection unit, or the like, and other (oralternative) elements used for writing precise servo patterns onsurfaces of the disk 702. Such a stable clock system may include aseparate clock head 734 that flies over one of the disk surfaces and aclock read/write channel 736 to provide a coherent clock signal. Thecontroller 720 can control the write currents provided to the writeelements. An identical write current can be provided to each of theheads 704 (and more specifically to the write element on each head), oreach head 704 can receive its own unique write current.

The media-writer 700 is likely sensitive to vibration, contamination,and electromagnetic interference. Accordingly, it is likely operated ona heavy granite anti-vibration table in a clean room that is itselfprotected from vibration and shock.

As mentioned above, the media-writer 700 can be used to write servopatterns on each disk 702 in the stack of disks 702. Each disk 702 canthen removed from the media-writer 700 and placed in a separate drivecontaining multiple blank disks, such that the drive can use thepatterned disk as a reference to re-write servo patterns on all of theother disk surfaces in the drive, as well as writing a servo pattern onthe patterned surface, if desired. The media-writer 700 is a relativelyexpensive instrument, and it may take a relatively long time for it towrite a reference pattern on the stack of disks 702. However, asmentioned above, if the stack contains many disks 702, e.g., ten disks,then the media-writer 700 can write the reference pattern for ten drivesin approximately the same time that it would have taken to servowrite asingle drive. It is also possible that the a media writer is used towrite the final patterns on the disk surface(s). Such disks can then beplaced in disk drives and used “as is” (i.e., without re-writing ofservo patterns).

Methods for using a media-writer to write servo burst patterns inaccordance with embodiments of the present invention will now besummarized with reference to FIG. 8A. As shown in FIG. 8A, step 802includes selecting one or more write elements from a plurality of writeelements (e.g., selecting N elements from a plurality of M elements,where M>N), that for a predetermined write current, produce servo burststhat have a width that is substantially equal to a desired width. Inaccordance with specific embodiments of the present invention, thedesired width is three-fourths of a desired data track width.

Step 802 can include testing the plurality of write elements by drivingeach write element using the predetermined current and measuringresulting burst widths, and selecting the write element(s) based on themeasured burst widths. Step 802 can alternatively, or additionally,include measuring the physical width of each write element, andselecting the write element based on the measured physical widths. It isnoted that the term “based on,” as used herein, is open ended in that itmeans “based at least in part on,” unless otherwise specified. Forexample, selecting a write element based on its width means that thewrite element may also be selected for other attributes in addition toits width.

Next, at step 804, the selected write element(s) is/are used in amedia-writer to write untrimmed servo burst patterns including servobursts that have the desired width. An exemplary media writer 700 wasdiscussed above. However, the present invention is not limited to usewith the exemplary media writer 700. Additional embodiments of thepresent invention, that can be used with a media-writer, are describedbelow.

Methods for controlling write currents to produce servo bursts having adesired width will now be summarized with reference to FIG. 8B.Referring to FIG. 8B, at a step 812, there is a determination of anappropriate write current that will cause a write element to produceservo bursts that have a width that is substantially equal to a desiredwidth. In accordance with embodiments of the present invention, thedesired width is three-fourths of a data track width.

Step 812 may include performing a calibration process to obtaininformation that correlates burst widths with write currents for thewrite element. This can include, producing a calibration table thatstores the information that correlates burst widths with write currentsfor the write element. The calibration table can then be used todetermine the appropriate write current that will cause the writeelement to produce servo bursts that have a width that is substantiallyequal to three-fourths of the desired data track width. Additionaldetails of an exemplary calibration process and table, according toembodiments of the present invention, were discussed above.

Next, at a step 814, the write element is supplied with the appropriatewrite current in order to write untrimmed servo burst patterns includingservo bursts that have a width that is substantially equal to thedesired width (e.g., three-fourths of the desired track width.).Embodiments of the present invention are also directed to combinationsof the methods of FIGS. 8A and 8B. For example, the method of FIG. 8Amay be used to select preferred write elements (e.g., elements that meeta high tolerance), while the method of FIG. 8B is used to fine tune thewrite burst width produced by each of preferred write elements. Further,it may be difficult or impossible to choose a single write element thatwrites desired burst widths across an entire stroke of the disk, due thechanges in the angle of the write element with respect to the disk asthe write element is moved along the stroke. Thus, the method of claim8B can be used to appropriately adjust the write current for a selectedpreferred write element as the write element moves across the stroke ofthe disk.

In accordance with an embodiment of the present invention, steps 812 and814 are performed by a media-writer. In accordance with anotherembodiment of the present invention, steps 812 and 814 are preformedunder the control of a servowriter, at a servowriter station. In stillanother embodiment of the present invention, steps 812 and 814 areperformed within a disk drive during self-servo writing.

Exemplary HDA at a Servowriter Station

Referring now to FIG. 9A, an exemplary HDA 931 is located at anexemplary servowriter station 932 (likely within a clean room) andplaced in registration with alignment pins 911. The exemplary head diskassembly (HDA) 931 includes at least one disk 902, an actuator assembly906, a read/write (R/W) head 904, a current pre-amplifier 916, a spindlemotor (SM) 932 and a voice coil motor (VCM) 930.

The HDA 930 likely also includes an opening formed in a base wall,sidewall or cover plate for admitting a mechanical or virtual (e.g.optical) push-pin 934 of the servowriter 932. The push-pin 934 has anengagement end which engages the actuator arm 906 and another endcoupled to a retro-reflector 936. The retro-reflector 936 reflects alaser beam back to a laser optics unit 938 within the servowriter 932.The laser optics unit 938 can use conventional laser interferometrytechniques to determine precise relative location of the retro-reflector936 relative to reference pins 911 and thereby indirectly determinesrelative position of the push-pin 934 and actuator arm 906 relative tothe disk 902. This relative position information is fed into an actuatorpush-pin controller unit 939 which controls position of the push-pin 934and thereby controls position of the actuator head arm 906 duringservowriter aided servowriting operations. Other position systemtechniques are possible, such as use of an optical encoder attached tothe push pin.

The servowriter 932 can control the SM 932, the VCM 930 and the R/W head904 via current pre-amplifier 916 in order respectively to rotate thedisk 902, position the actuator 906 and write and possibly check digitalservo information fields and servo burst patterns on the disk(s) 902.The servowriter 932 may also include a clock head (not shown) that isinserted through an opening in the HDA 930 such that the clock headflies over one of the disk surfaces, to provide a coherent clock signal.

In accordance with an embodiment of the present invention, a servowriter(such as the servowriter 932) is used to write the final servo burstpatterns shown in FIG. 3. Alternatively, the servowriter can be used towrite initial reference servo burst patterns that are later used duringself-servo writing to write the final servo burst patterns shown in FIG.3.

After the servo burst pattern (final or initial) is written at theservowriter station 932, the HDA 931 is sealed relative to the ambientatmosphere (e.g., by placement of a protective stickers over thepush-pin opening and a clock track head opening in the base wall,sidewall or cover plate).

The sealed HDA 931 can then be moved (e.g., from the clean roomenvironment) to an assembly station at which a drive circuit board 950carrying disk drive electronics may be mounted to and electricallyconnected to the HDA 931, as shown in FIG. 9B, discussed below. It isalso possible that a disk drive is produced without ever using aservowriting station. This is becoming more prevalent as self-servowriting is becoming the preferred scheme for writing all servoinformation.

Exemplary Disk Drive

Referring to FIG. 9B, a drive circuit board 950 typically includes a R/Wchannel 914, a SM driver 912, a VCM driver 908, a microprocessor 920,and a disk controller 928. More or fewer chips may actually be includedon the board 950, depending upon the particular circuit integration atthe chip/board level. Various combinations of the blocks shown in FIG.9B may be integrated onto common chips (or onto a single chip). Thedrive electronics printed circuit board 950 is attached to the HDA 931and connected to the R/W head 904 via the preamplifier 916, SM 932 andVCM 930, and the R/W channel 914 is connected to the read and writeelements of the R/W head 904 via the preamplifier 916. A structurallycompleted hard disk drive 900 results.

The completed disk drive 900 can then moved to a self-scan unit. Theself-scan unit can include a diskware download station 954 fordownloading disk control software, including self-servo-write controlsoftware, from a central computer, e.g. to reserved tracks for retrievaland execution by the drive's digital controller on the circuit board950. These reserved tracks may be completely servowritten to enableeasier code writing for the completed hard disk drive 900.Alternatively, the disk control firmware can be stored in electricallyprogrammable read only memory (not specifically shown) on the drive'scircuit board 950, or it can be downloaded to the drive via a serialport facility included as an additional part of the drive electronics.

Alternatively, a special circuit board may be connected to the R/W head904 via preamplifier 916, the SM 932, and the VCM 930. This specialcircuit board would typically include the functions identified inassociation with the disk drive product circuit board 950 shown in FIG.9B, but would be specially adapted for drive self-servo-writingoperation, and therefore typically be endowed with greater computingspeed and capacity than the drive circuit board 950, enabling use ofmultiple self-written servo bursts and multi-rate servo pattern samplingtechniques, etc., in order to self-write a final burst pattern. Afterthe final product servo patterns are self-written, the special circuitboard would be disconnected, and the drive circuit board 950 would beinstalled and connected, thereby completing disk drive assembly.Diskware download via the function 954 could then occur via theinterface or a separate serial port of the circuit board 950, ordiskware could be downloaded via the specialized circuit board.Alternatively, the circuit board 950 could be pre-programmed to containthe drive's operating firmware before being mated to a servo-writtenHDA.

The assembled drive 900 can remain at the self-scan station for severalhours. The self-scan process may require many hours to carry out theself-servowriting processes of the present invention. In accordance withembodiments of the present invention, by the time the disk drive 900leaves the self-scan unit, the final servo burst patterns will have beenself-written to the disk(s) 902.

In accordance with an embodiment of the present invention, the finalpreferred servo patterns are self servo-written while the disk drive 900is at the self-scan unit/station. More specifically, in accordance withan embodiment of the present invention, the servo burst patterns shownin FIG. 3 are written entirely during self servo-writing. Alternatively,initial reference servo burst patterns can be written by a servowriter,which are later used during self-servo writing to write the final servoburst patterns shown in FIG. 3.

Completion of the disk drive will typically also include testing of theheads, media, mechanics, etc. tuning up read-channel characteristics, aswell as scanning of the disk surfaces to identify defective areas. Oncethe disk drive 900 is complete, the disk controller 928 can acceptinformation from a host 922 and can control many disk functions. Thehost 922 can be any device, apparatus, or system capable of utilizingthe disk drive 900, such as a personal computer, Web server or consumerelectronics device. The disk controller 928 can include an interfacecontroller in some embodiments for communicating with the host 922, andin other embodiments a separate interface controller can be used.

The microprocessor 920 can also include a servo system controller, whichcan exist as circuitry within the drive or as an algorithm resident inthe microprocessor 920, or as a combination thereof. In otherembodiments, an independent servo controller can be used. Additionally,the microprocessor 920 may include some amount of memory such as SRAM,or an external memory such as SRAM 910 can be coupled with themicroprocessor 920. The disk controller 928 can also provide user datato the read/write channel 914, which can send signals to the currentamplifier or preamp 916 to be written to the disk 902, and can sendservo signals to the microprocessor 920. The disk controller 928 canalso include a memory controller to interface with memory 918. Memory918 can be DRAM, which in some embodiments, can be used as a buffermemory.

Although shown as separate components, the VCM driver 908 and spindlemotor driver 912 can be combined into a single “hard disk power-chip.”It is also possible to include the spindle speed control circuitry inthat chip. The microprocessor 920 is shown as a single unit directlycommunicating with the VCM driver 908, although a separate VCMcontroller processor (not shown) may be used in conjunction withprocessor 920 to control the VCM driver 908. Further, the processor 920can directly control the spindle motor driver 912, as shown.Alternatively, a separate spindle motor controller processor (not shown)can be used in conjunction with microprocessor 920.

A drive head position servo control loop uses the final product embeddedservo patterns written to each data storage surface, and structurallyincludes the read element of the head 904 associated with a particularsurface, the preamplifier 916, the read/write channel 914, the diskcontroller 928, the microprocessor 920, the VCM driver 908, the VCM 930and the actuator assembly 906. Various analog to digital converters anddigital to analog converters and other processing circuitry are alsoincluded within the head position servo control loop as is wellunderstood by those skilled in the art and therefore not describedherein in any further detail.

Although embodiments described herein refer generally to systems havinga read/write head that can be used to write bursts on rotating magneticmedia, other embodiments of the invention can take advantage of similarvariation, such as variations in drive current or drive voltage. Forexample, a laser writing information to an optical media can be drivenwith variable power in order to increase or decrease pit width in themedia in order to reduce track variation. Any media, or at least anyrotating media, upon which information is written, placed, or stored,may be able to take advantage of embodiments of the invention, asvariations in optical, electrical, magnetic, mechanical, and otherphysical systems can be made by varying a drive signal or other controlmechanism in order control a write width.

The foregoing description of preferred embodiments of the presentinvention has been provided for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many modifications andvariations will be apparent to one of ordinary skill in the relevantarts. The embodiments were chosen and described in order to best explainthe principles of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications that are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims and their equivalence.

1. A method for writing servo burst patterns on a surface of a disk foruse in a disk drive, comprising: (a) selecting a write element from aplurality of write elements, that for a predetermined write current,produces untrimmed servo bursts that have a width that is substantiallyequal to three-fourths of a desired data track width (DTW); and (b)using the selected write element in a media-writer to write untrimmedservo burst patterns including untrimmed servo bursts that have a widththat is substantially equal to three-fourths of the desired DTW.
 2. Themethod of claim 1, wherein step (a) includes testing the plurality ofwrite elements by driving each write element using the predeterminedcurrent and measuring resulting burst widths, and selecting the writeelement based on the measured burst widths.
 3. The method of claim 1,wherein step (a) includes measuring the physical width of each writeelement, and selecting the write element based on the measured physicalwidths.
 4. The method of claim 1, wherein the desired DTW ispredetermined.
 5. The method of claim 4, wherein the desired DTW isabout 0.25 μm.
 6. A method for writing servo burst patterns on a surfaceof a disk for use in a disk drive, comprising: (a) selecting a writeelement from a plurality of write elements, that for a predeterminedwrite current, produces untrimmed servo bursts that have a desiredwidth; and (b) using the selected write element in a media-writer towrite untrimmed servo burst patterns including untrimmed servo burststhat have the desired width.
 7. A method for writing servo burstpatterns on a surface of a disk for use in a disk drive, comprising: (a)selecting a write element from a plurality of write elements thatproduces untrimmed servo bursts that have a width that is within athreshold of a desired width; (b) determining an appropriate writecurrent that will cause the selected write element to produce untrimmedservo bursts that have the desired width; and (c) supplying the writeelement with the appropriate write current in order to write untrimmedservo burst patterns including untrimmed servo bursts that have thedesired width.
 8. The method of claim 7, wherein step (b) includesperforming a calibration process to obtain information that correlatesburst widths with write currents for the selected write element.
 9. Themethod of claim 8, wherein step (b) includes producing a calibrationtable that stores the information that correlates burst widths withwrite currents for the selected write element.
 10. The method of claim9, wherein step (b) includes using the calibration table to determinethe appropriate write current that will cause the selected write elementto produce untrimmed servo bursts that have the desired width.
 11. Amethod for writing servo burst patterns on a surface of a disk for usein a disk drive, comprising: (a) selecting a write element from aplurality of write elements, that for a predetermined write current,produces untrimmed servo bursts that have a width that is substantiallyequal to a desired width; and (b) adjusting a write current provided tothe selected write element as the write element is moved across a strokeof the disk such that the write element produces untrimmed servo burststhat have a width substantially equal to the desired width, across thestroke of the disk.
 12. A method for writing servo burst patterns on asurface of a disk for use in a disk drive, comprising: (a) determiningan appropriate write current that will cause a write element to produceuntrimmed servo bursts that have a width that is substantially equal tothree-fourths of a desired data track width (DTW); and (b) supplying thewrite element with the appropriate write current in order to writeuntrimmed servo burst patterns including untrimmed servo bursts thathave a width that is substantially equal to three-fourths of the desiredDTW.
 13. The method of claim 11, wherein step (a) includes performing acalibration process to obtain information that correlates burst widthswith write currents for the write element.
 14. The method of claim 13,wherein step (a) includes producing a calibration table that stores theinformation that correlates burst widths with write currents for thewrite element.
 15. The method of claim 14, wherein step (a) includesusing the calibration table to determine the appropriate write currentthat will cause the write element to produce untrimmed servo bursts thathave a width that is substantially equal to three-fourths of the desiredDTW.
 16. The method of claim 12, wherein steps (a) and (b) are performedby a media-writer.
 17. The method of claim 12, wherein steps (a) and (b)are preformed under the control of a servowriter.
 18. The method ofclaim 12, wherein steps (a) and (b) are performed within a disk driveduring self-servo writing.
 19. The method of claim 12, wherein thedesired DTW is predetermined.
 20. The method of claim 19, wherein thedesired DTW is about 0.25 μm.
 21. The method of claim 12, wherein thedesired DTW varies for different positions along a stroke the diskdrive.
 22. A method for writing servo burst patterns on a surface of adisk for use in a disk drive, comprising: (a) determining an appropriatewrite current that will cause a write element to produce untrimmed servobursts that have a desired width; and (b) supplying the write elementwith the appropriate write current in order to write untrimmed servoburst patterns including untrimmed servo bursts that have the desiredwidth.
 23. The method of claim 22, wherein step (a) includes performinga calibration process to obtain information that correlates burst widthswith write currents for the write element.
 24. The method of claim 23,wherein step (a) includes producing a calibration table that stores theinformation that correlates burst widths with write currents for thewrite element.
 25. The method of claim 24, wherein step (a) includesusing the calibration table to determine the appropriate write currentthat will cause the write element to produce untrimmed servo bursts thathave the desired width.
 26. The method of claim 22, wherein steps (a)and (b) are performed by a media-writer.
 27. The method of claim 22,wherein steps (a) and (b) are preformed under the control of aservowriter.
 28. The method of claim 22, wherein steps (a) and (b) areperformed within a disk drive during self-servo writing.
 29. The methodof claim 22, wherein the desired DTW is predetermined.
 30. The method ofclaim 29, wherein the desired DTW is about 0.25 μm.
 31. The method ofclaim 22, wherein the desired DTW varies for different positions along astroke the disk drive.
 32. A method for writing servo burst patterns ona surface of a disk for use in a disk drive, comprising: (a) writing afirst untrimmed servo burst having a width that is substantially equalto three-fourths of a desired data track width (DTW); (b) writing asecond untrimmed servo burst circumferentially adjacent said first servoburst, said second servo burst having and upper edge radially offsetfrom an upper edge of said first servo burst by substantially one-halfof the desired DTW, said second servo burst also having a width that issubstantially equal to three-fourths of the desired DTW; (c) writing athird untrimmed servo burst circumferentially adjacent said second servoburst, said third servo burst having and upper edge radially offset fromthe upper edge of said second servo burst by substantially one-half ofthe desired DTW, said third servo burst also having a width that issubstantially equal to three-fourths of the desired DTW; and (d) writinga fourth untrimmed servo burst circumferentially adjacent said thirdservo burst, said fourth servo burst having and upper edge radiallyoffset from the upper edge of said fourth servo burst by substantiallyone-half of the desired DTW, said fourth servo burst also having a widththat is substantially equal to three-fourths of the desired DTW.
 33. Themethod of claim 32, wherein steps (a) through (d) are performed bymedia-writer.
 34. The method of claim 32, wherein steps (a) through (d)are preformed under the control of a servowriter.
 35. The method ofclaim 32, wherein steps (a) through (d) are performed within a diskdrive during self-servo writing.
 36. The method of claim 32, wherein awrite element is used to write said first, second, third and fourthuntrimmed servo bursts; and wherein the widths of said untrimmed servobursts are controlled by: determining an appropriate write current thatwill cause the write element to produce untrimmed servo bursts that havea width that is substantially equal to three-fourths of the DTW; andsupplying the write element with the appropriate write current duringsteps (a) through (d).
 37. The method of claim 32, wherein a writeelement is used to write said first, second, third and fourth untrimmedservo bursts, and further comprising: radially moving said write elementone-half of the desired DTW between steps (a) and (b); radially movingsaid write element one-half of the desired DTW between steps (b) and(c); and radially moving said write element one-half of the desired DTWbetween steps (c) and (d).
 38. The method of claim 37, wherein steps (a)through (d) are part of a two-step-per-track servowriting process. 39.The method of claim 32, wherein the desired DTW is predetermined. 40.The method of claim 39, wherein the desired DTW is about 0.25 μm. 41.The method of claim 40, wherein the desired DTW varies for differentpositions along a stroke the disk drive.
 42. The method of claim 32,repeating steps (a) through (d) across the surface of the disk.